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Nexus fermions in topological symmorphic crystalline metals

TitleNexus fermions in topological symmorphic crystalline metals
Publication TypeJournal Article
Year of Publication2017
AuthorsChang, Guoqing, Xu Su-Yang, Huang Shin-Ming, Sanchez Daniel S., Hsu Chuang-Han, Bian Guang, Yu Zhi-Ming, Belopolski Ilya, Alidoust Nasser, Zheng Hao, Chang Tay-Rong, Jeng Horng-Tay, Yang Shengyuan A., Neupert Titus, Lin Hsin, and Hasan Zahid M.
JournalSci Rep
Date Published05/2017
Keywordsarcs, dirac semimetals, discovery, niobium, nitrides, tantalum, wc, weyl

Topological metals and semimetals (TMs) have recently drawn significant interest. These materials give rise to condensed matter realizations of many important concepts in high-energy physics, leading to wide-ranging protected properties in transport and spectroscopic experiments. It has been wellestablished that the known TMs can be classified by the dimensionality of the topologically protected band degeneracies. While Weyl and Dirac semimetals feature zero-dimensional points, the band crossing of nodal-line semimetals forms a one-dimensional closed loop. In this paper, we identify a TM that goes beyond the above paradigms. It shows an exotic configuration of degeneracies without a welldefined dimensionality. Specifically, it consists of 1D nexus with triple-degeneracy that interconnects 1D lines with double-degeneracy. We show that, because of the novel form of band crossing, the new TM cannot be described by the established results that characterize the topology of the Dirac and Weyl nodes. Moreover, triply-degenerate nodes realize emergent fermionic quasiparticles not present in relativistic quantum field theory. We present materials candidates. Our results open the door for realizing new topological phenomena and fermions including transport anomalies and spectroscopic responses in metallic crystals with nontrivial topology beyond the Weyl/ Dirac paradigm.


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